Multiphase motor with magnetized rotor having N pairs of poles with axial magnetization

ABSTRACT

The motor structure is as follows: 
     the rotor (1) has N magnetization axes parallel to the axis of rotation of the rotor, the adjacent poles having opposite polarities; 
     the stator (2) forms m phases (r, s), m=N/2n, for n being an integer; 
     every phase (r, s) comprises a pair of coplanar polar pieces (3, 4) interpositioned, the one (3) in the other one (4), 
     the polar pieces (3, 4) comprise full poles (p 1  to p 4  and p 6  to p 8 ) and fractional poles (p 5 , p 9 ); 
     the phases (r, s) are displaced with respect to one another; 
     the polar pieces (3, 4) of every phase (r, s) are magnetically connected with one another by a coiled core (7).

This invention relates to multiphase motors, the rotor of which has Npairs of poles with axial magnetization.

Different types of motors with magnetized rotors exist. According to thepresent invention the magnetization axes of the rotor is parallel to therotation axis of the rotor.

A principal object of the invention is to create a multiphase motor witha high efficiency by using existing materials, and which is easilymanufactured by industrial processes and the phase number of which, aswell as the range of powers, can be very extensive without modifying themotor conception. Subsidiarily, the invention also has as its object tocreate a multiphase motor which can easily be adapted to the steppingmode.

The field of applications of the motor according to the invention isthus very large. This motor can particularly be used with drivingsystems for office automation, robots, aeronautical and space industry,photographic installations and time-keepers. More generally, the motoraccording to the present invention is suitable to all the systems usingdigital techniques, and, more particularly, to all those with which sizeoutput power and speed constitute critical criteria.

One embodiment of the motor according to the invention and two variantsare represented schematically and simply by way of example in thedrawings in which:

FIG. 1 is a view of that embodiment in the direction of the rotationaxis of the rotor;

FIG. 2 is a plan view of its stator;

FIG. 3 is a plan view of its rotor;

FIG. 4 is a perspective view of this rotor;

FIG. 5 is a view similar to that of FIG. 4, but relating to the firstvariant;

FIG. 6 is a plan view of a piece of the second variant;

FIGS. 7 and 8 are linear unrollings of the motor which illustrate itsmode of operation.

The motor represented in FIGS. 1 to 4 has a rotor 1 provided with anumber N of pairs of poles equal to eight. The number m of the phases ofthis motor is equal to two. Moreover, the shifting between these twophases is equal to 2τ/(N·m).

The rotor 1 is of ferromagnetic material such as samarium-cobalt, thecoercive force of which is high and the specific mass small. It haseight pairs of poles, the magnetization axes of which are parallel tothe rotation axis of the rotor, but alternately in opposite directions,and they are regularly arranged around that axis.

The rotor 1 is mounted opposite a stator 2 which forms two phases r ands. Each phase r, s comprises two polar pieces 3, 4 coplanar,interpositional in one another, piece 3 being within piece 4. The twopolar pieces 3, 4 are separated from one another by a sinuous air-gap 5in each phase.

The polar pieces 3, 4 are of ferromagnetic material having a smallcoercive force and a high saturation induction. They have poles 6(FIG. 1) which are designated by p₁, p₂, . . . , p₉ in FIG. 2 tofacilitate the explanation.

FIG. 2 shows that the poles p₁, p₃ of polar piece 4 of phase r, thepoles p₂, p₄ of polar piece 3 of this same phase r, poles p₆, p₈ ofpolar piece 4 of phase s and pole p₇ of this same phase s have, eachone, the same arc. These different poles are called full poles, whereaspoles p₅ and p₉ of polar piece 3 of phase s are fractional poles. Thesum of the angular extensions of these two fractional poles is at leastapproximately equal to the angular extension of a full pole.

In the general case of a motor with m phases, the rotor of which has Npairs of poles, the poles of the polar pieces of m-1 phases and those ofone polar piece of the mth phase are full; they are 1/2 N/m in numberper polar piece and they are arranged at an angular interval at leastapproximately equal to twice that between the pairs of adjacent poles ofthe rotor. Regarding the poles of the remaining polar piece, there are(1/2 N/m)-1 which are full, whereas the m remaining poles arefractional, the sum of their arcs being at least approximately equal tothe arc of a full pole.

With the embodiment represented, one of the phases r, s is displacedwith respect to the other one through an angle α.sub.γ of 22.5°. In thegeneral case of a motor with m phases, the rotor of which has N polepairs, α.sub.γ =2π/Nm. The arc of every fractional pole is at leastapproximately equal to 1/m times that of a full pole.

The displacement α.sub.γ can be made different from 2π/Nm. In this case,the sum of the arcs of the fractional poles remains at leastapproximately equal to the arc of a full pole, but all these fractionalpoles no longer have the same arc.

The two polar pieces of each phase of stator 2 are magneticallyconnected to one another by a core 7 of ferromagnetic material having asmall coercive force and a high saturation induction. A coil 8 is woundaround the core of each phase.

The polar pieces 3, 4 of each phase can be positioned each one by a pinand a threaded foot (not shown). Regarding mounting the rotor 1, it isconventional. It can be journaled in bearings having a small slidingfriction. Its shaft (not shown) can carry a pinion meshing with a firstwheel of a wheel gear to transmit the rotor rotations to the gear.

In the first variant (FIG. 5), a disk 9 of soft ferromagnetic materialis secured to the face of the rotor opposed to that facing the stator.

In the variant of FIG. 6, the motor comprises a fixed soft ferromagneticdisk which is mounted so that the rotor will be located between thatdisk and the stator. That disk is provided with openings 10 which arejudiciously located in order to produce a positioning torque.

FIGS. 7 and 8 illustrate the operation of the motor. They are lineardeveloped views thereof. More particularly, they are diagrammaticsections linearly unrolled. The shift of the phases r, s is 22.5°.

FIG. 8 shows the state of the motor when the rotor has moved through22.5° with respect to that represented in FIG. 7, i.e., in the generalcase, through an angle α.sub.γ =2π/Nm.

In order to facilitate understanding the operation of the motorrepresented, the manner to determine the characteristic curve calledmutual torque is first disclosed. The mutual torque is that due to theinteraction between the magnetic fluxes of the rotor and those of thecoils.

In the position of FIG. 7, poles of the rotor 1 are exactly oppositepoles p₁, p₂, p₃ and p₄ of phase r. That Figure shows that the rotorfluxes directed toward the stator are received by poles p₂ and p₄ ofpolar piece 3, from which they are directed to core 7 of phase r,through which they flow from B to A. They are then closed by passingthrough poles p₁ and p₃ of polar piece 4 of the stator. Regarding therotor fluxes directed in the opposed directon, they are also received bypolar piece 3 of phase r and are consequently directed along the samepath as that of the first ones considered. Thus, they flow through core7 also from B to A before they get closed. In the considered rotorposition, the rotor flux through core 7 of phase r is thus maximum.

Upon moving the rotor from that position through an angle α.sub.ρ equalto 2π/N, it is easy to see that the flux through core 7 of phase r ismaximum too, but in the opposite direction, i.e., it flows through thiscore from A to B. There is thus a reversal of the rotor flux in core 7of phase r, every time the rotor turns through an angle equal to 2π/N,of 45° in the example represented.

When the coil of phase r is driven, an interaction torque resultsbetween the coil and the magnetized rotor, the mutual torque, the periodof which is equal to 4π/N, and the neutral positions of which correspondto the rotor positions in which the poles of the rotor are exactlyopposite the poles of the polar pieces of this phase r.

Regarding poles p₅, p₆, p₇, p₈ and p₉ of phase s, between which are thepoles of the rotor in FIG. 7, it is easy to see that this phase s alsohas a mutual torque with a period of 4π/N, but displaced with respect tothe mutual torque of phase r through an angle α.sub.γ =2π/Nm, of 22.5°in the example represented.

The rotor position in which its flux through core 7 of phase s ismaximum in that of FIG. 8. The two fractional poles p₅ and p₉ eachreceive a flux equal to 1/m times the flux received by a full pole, thus1/2 times that of a full pole in the presented example.

The remarks made here above with respect to an angular displacement ofthe phases different from 2π/Nm are applicable here too.

The motor behavior with the indicated mutual torques, when the coils aredriven, is known and will not be disclosed.

The two-phase motor represented with a rotor having eight pairs of polesis obviously not the only possible embodiment of the motor according tothe invention. The relation m=N/2n between the number N of pole pairs ofthe rotor and that m of the phases, n being an integer, need only besatisfied. The following table indicates the possible configurations ofthe motor according to the invention.

    ______________________________________                                        m                  n     N                                                    ______________________________________                                        2                  1      4                                                   two-phase          2      8                                                                      3     12                                                                      4     16                                                                      . . . . . .                                                                   . . . . . .                                                3                  1      6                                                   three-phase        2     12                                                                      3     18                                                                      4     24                                                                      . . . . . .                                                                   . . . . . .                                                4                  1      8                                                   four-phase         2     16                                                                      3     24                                                                      4     32                                                                      . . . . . .                                                                   . . . . . .                                                . . .              . . . . . .                                                                   . . . . . .                                                ______________________________________                                    

With the first variant represented in FIG. 5, the presence of the softferromagnetic disk 9 on the rotor has an effect to increase the flux ofevery pair of rotor poles by increasing the permeance from the viewpoint of the rotor.

The fixed ferromagnetic disk of the second variant represented in FIG. 6has an analogous effect. Moreover, it overbalances the attractionbetween the rotor and the stator. The openings 10 of this disk have aseffect to generate a positioning torque. The openings are equal innumber to that of the pole pairs of the rotor and they are regularlydistributed to form a circular row concentric to the rotor. In thiscase, the period of the positioning torque is equal to 2π/N. However, itwould also be possible to generate a positioning torque with a period of4π/N by suppressing every other opening 10.

Regarding the efficiency of the motor according to the invention andwithout going into the details of the theory, those skilled in the artwill note that it is high.

At first, the fluxes of all the pole pairs of the rotor flow in the samedirection through each coil core, because of the disclosedinterpositioning of polar pieces 3, 4, of the magnetic connectionprovided between the two polar pieces and of the provision of full andfractional poles. There is, indeed, no pole pair of the rotor, the fluxof which would be lost, i.e. would not be closed through the cores andwould not contribute in additive manner to the mutual flux.

Moreover, when the motor operates stepwise, the fact that the rotor isplain, i.e. has no angular gap between the magnetization axes whichwould not be equal to 2π/N, optimizes, from the view point of theefficiency, the relation between the total flux of the pole pairs of therotor and the inertia of the rotor. That is due to the fact that theefficiency is a function increasing with the flux and decreasing withthe inertia, but that the power to which that function increases withthe flux is higher than that to which it decreases with the inertia.

The phase number of the motor according to the invention can be verygreat without modifying the motor concept, since it suffices that therelation m=N/2n be satisfied for n being an integer. In other words, itsuffices to increase the number N of pole pairs of the rotor in order toincrease the number m of phases.

The motor according to the invention also has the advantage of offeringa very large range of powers, without having to modify the motorconcept. Without going into the details of theory, it is, indeed,intuitive to observe that the mechanical power of a motor of this typeis a function increasing with the number of pole pairs of the rotor aswell as with the diameter of the rotor.

The manufacture of the motor according to the invention is easy, sinceits stator is wholly determined in a plane.

Finally, the motor according to the invention has the advantage of beingsuitable to the stepping mode of operation, since the disk of FIG. 6permits the entry of the positioning torque required by that operationmode.

I claim:
 1. A multiphase motor with a magnetized rotor having N pairs ofrotor poles, the axis of magnetization of each rotor pole being parallelto the axis of rotation of said rotor,wherein the magnetization axes ofthe rotor poles are regularly distributed around the axis of rotation ofsaid rotor, the adjacent rotor poles having opposite polarities, whereinthe rotor is mounted opposite a stator, said stator formed with m phaseswhere m=N/2n, n being an integer and m being an integer greater that 1,each phase comprising two substantially coplanar polar pieces, one ofwhich is interpositioned in the other one and being separated therefromby a sinuous air-gap, wherein for m-1 phases as well as for a firstpolar piece of the remaining phase, the stator poles of every polarpiece, being n=N/2m in number, are full and spaced apart by an angularinterval at least approximately two times larger than that between theadjacent rotor poles, (N/2m)-1 stator poles of a second polar piece ofthe remaining phase being full, wherein the m remaining stator poles ofsaid second polar piece are fractional, the sum of the arcs of allfractional stator poles being at least approximately equal to the arc ofa full pole, wherein the phases are phase-shifted with respect to oneanother, wherein the two polar pieces of every phase are magneticallyconnected to first and second ends, respectively, of a respective core,and wherein each core has at least one coil wound thereon.
 2. A motoraccording to claim 1, wherein the phases are phase-shifted with respectto one another through an angle at least approximately equal to 2π/Nmand wherein the arc of every fractional pole is at least approximatelyequal to 1/m times that of a full pole.
 3. A motor according to claims 1or 2, further including a soft ferromagnetic disk fixed to the face ofthe rotor which is opposite that facing the stator.
 4. A motor accordingto one of the claims 1 or 2 further including a fixed soft ferromagneticdisk located so that the rotor lies between the disk and the stator. 5.A motor according to claim 4, wherein the fixed soft ferromagnetic diskhas N openings regularly distributed to form a circular now concentricto the disk.
 6. A motor according to claim 4, wherein the fixed softferromagnetic disk has N/2 openings regularly distributed to form acircular row concentric to the disk.